(1) Field of the Invention
The invention generally relates to amination reactions and reaction products, and particularly to methods for aminating vinyl aromatic polymers utilizing tertiary amines. Such methods and reaction products are useful for preparing ion exchange resins.
(2) Description of the Related Art
Vinyl aromatic polymers are commonly functionalized with amine groups by way of “amination reactions,” i.e. wherein a polymer is reacted with an amine to form an aminated reaction product. A common example is the preparation of ion exchange resin wherein a chloromethylated vinyl aromatic polymer is reacted with an amine to form an ion exchange resin including functional amine groups. Examples of such amination reactions are provided in: U.S. Pat. No. 5,134,169; U.S. Pat. No. 6,756,462; U.S. Pat. No. 6,924,317; U.S. Pat. No. 7,282,153; and US 2004/0256597. Aminations may be performed using primary, secondary or tertiary amines, or combinations; see for example U.S. Pat. No. 5,141,965 which discloses a sequential amination of a chloromethylated crosslinked vinyl aromatic polymer with a primary or secondary amine followed by a subsequent amination with a tertiary amine, U.S. Pat. No. 3,317,313 which discloses a sequential amination including a first amination with a tertiary amine followed by an amination with a secondary amine, and U.S. Pat. No. 6,059,975 which discloses amination with a tertiary amine having relatively large (≧C5) alkyl groups followed by a second amination with a tertiary amine having smaller alkyl groups. The entire subject matter of each of the US patents listed above are incorporated herein by reference.
Commercially available examples of vinyl aromatic polymers aminated with tertiary amines include: DOWEX™ 1 brand ion exchange resin, a strong base, gel-type resin comprising a crosslinked styrene-divinylbenzene copolymer matrix with quaternary ammonium functionality (i.e. functional groups produced via reaction between a chloromethylated styrene-divinylbenzene copolymer matrix and a trimethyl amine); DOWEX™ SAR brand ion exchange resin (produced via reaction between a chloromethylated styrene-divinylbenzene copolymer matrix and a dimethylethanol amine); DOWEX™ PSR-2 brand resin, a strong base, gel-type resin (produced via reaction between a chloromethylated styrene-divinylbenzene copolymer matrix and tri-n-butyl amine); and DOWEX™ PSR-3 brand resin is a strong base, macroporous resin (produced via reaction between a chloromethylated styrene-divinylbenzene copolymer matrix and tri-n-butyl amine).
Ion exchange resins produced by amination with tertiary amines often suffer from low conversion (i.e. lower yields of the desired aminated reaction product as compared with aminations with primary or secondary amines) and “bead” or polymer particle breakage. These problems are even more pronounce when aminating with “bulky” tertiary amines. That is, tertiary amines having 7 or more carbon atoms, but particularly 8 or more carbon atoms (e.g. tripropyl amine, tributyl amine, etc.) have significant steric hindrance (and poor water solubility) which slows reaction with available benzyl chloride groups of the vinyl aromatic polymer. While the use of relatively high stoichiometric ratios of amine (e.g. greater than 1.5 mole of amine per mole of benzyl chloride group) can improve conversion, the use of such high ratios of amine is expensive and results in the loss of amine, or requires the use of amine recovery techniques.